Set SYSRESETREQ repeatedly on M55+M85+M52 (#214)

Fixes #195

Author: kjbracey

CMSIS/Core/Include/core_cm52.h

@@ -4125,16 +4125,18 @@ __STATIC_INLINE uint32_t __NVIC_GetVector(IRQn_Type IRQn)
  */
 __NO_RETURN __STATIC_INLINE void __NVIC_SystemReset(void)
 {
-  __DSB();                                                          /* Ensure all outstanding memory accesses included
-                                                                       buffered write are completed before reset */
-  SCB->AIRCR  = (uint32_t)((0x5FAUL << SCB_AIRCR_VECTKEY_Pos)    |
-                           (SCB->AIRCR & SCB_AIRCR_PRIGROUP_Msk) |
-                            SCB_AIRCR_SYSRESETREQ_Msk    );         /* Keep priority group unchanged */
-  __DSB();                                                          /* Ensure completion of memory access */
-
-  for(;;)                                                           /* wait until reset */
+  /* SYSRESETREQ needs to be set repeatedly as it is cleared as soon as the CPU's P-channel
+   * enters WARM_RST state, but another device can deny the transition preventing the
+   * actual reset. Such denials are usually transient - we need to re-assert SYSRESETREQ
+   * to retry.
+   */
+  for(;;)
   {
-    __NOP();
+    __DSB();                                                        /* Ensure all outstanding memory accesses included
+                                                                       buffered write are completed before reset */
+    SCB->AIRCR  = (uint32_t)((0x5FAUL << SCB_AIRCR_VECTKEY_Pos)    |
+                             (SCB->AIRCR & SCB_AIRCR_PRIGROUP_Msk) |
+                              SCB_AIRCR_SYSRESETREQ_Msk    );       /* Keep priority group unchanged */
   }
 }
 

CMSIS/Core/Include/core_cm55.h

@@ -4238,16 +4238,18 @@ __STATIC_INLINE uint32_t __NVIC_GetVector(IRQn_Type IRQn)
  */
 __NO_RETURN __STATIC_INLINE void __NVIC_SystemReset(void)
 {
-  __DSB();                                                          /* Ensure all outstanding memory accesses included
-                                                                       buffered write are completed before reset */
-  SCB->AIRCR  = (uint32_t)((0x5FAUL << SCB_AIRCR_VECTKEY_Pos)    |
-                           (SCB->AIRCR & SCB_AIRCR_PRIGROUP_Msk) |
-                            SCB_AIRCR_SYSRESETREQ_Msk    );         /* Keep priority group unchanged */
-  __DSB();                                                          /* Ensure completion of memory access */
-
-  for(;;)                                                           /* wait until reset */
+  /* SYSRESETREQ needs to be set repeatedly as it is cleared as soon as the CPU's P-channel
+   * enters WARM_RST state, but another device can deny the transition preventing the
+   * actual reset. Such denials are usually transient - we need to re-assert SYSRESETREQ
+   * to retry.
+   */
+  for(;;)
   {
-    __NOP();
+    __DSB();                                                        /* Ensure all outstanding memory accesses included
+                                                                       buffered write are completed before reset */
+    SCB->AIRCR  = (uint32_t)((0x5FAUL << SCB_AIRCR_VECTKEY_Pos)    |
+                             (SCB->AIRCR & SCB_AIRCR_PRIGROUP_Msk) |
+                              SCB_AIRCR_SYSRESETREQ_Msk    );       /* Keep priority group unchanged */
   }
 }
 

CMSIS/Core/Include/core_cm85.h

@@ -4262,16 +4262,18 @@ __STATIC_INLINE uint32_t __NVIC_GetVector(IRQn_Type IRQn)
  */
 __NO_RETURN __STATIC_INLINE void __NVIC_SystemReset(void)
 {
-  __DSB();                                                          /* Ensure all outstanding memory accesses included
-                                                                       buffered write are completed before reset */
-  SCB->AIRCR  = (uint32_t)((0x5FAUL << SCB_AIRCR_VECTKEY_Pos)    |
-                           (SCB->AIRCR & SCB_AIRCR_PRIGROUP_Msk) |
-                            SCB_AIRCR_SYSRESETREQ_Msk    );         /* Keep priority group unchanged */
-  __DSB();                                                          /* Ensure completion of memory access */
-
-  for(;;)                                                           /* wait until reset */
+  /* SYSRESETREQ needs to be set repeatedly as it is cleared as soon as the CPU's P-channel
+   * enters WARM_RST state, but another device can deny the transition preventing the
+   * actual reset. Such denials are usually transient - we need to re-assert SYSRESETREQ
+   * to retry.
+   */
+  for(;;)
   {
-    __NOP();
+    __DSB();                                                        /* Ensure all outstanding memory accesses included
+                                                                       buffered write are completed before reset */
+    SCB->AIRCR  = (uint32_t)((0x5FAUL << SCB_AIRCR_VECTKEY_Pos)    |
+                             (SCB->AIRCR & SCB_AIRCR_PRIGROUP_Msk) |
+                              SCB_AIRCR_SYSRESETREQ_Msk    );       /* Keep priority group unchanged */
   }
 }